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Date: Mon, 09 Dec 2002 18:01:41 -0800
From: Ken Rose <kenarose@earthlink.net>
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To: Daniel de Rauglaudre <daniel.de_rauglaudre@inria.fr>
CC: caml-list@inria.fr
Subject: Re: [Caml-list] Camlp4: generating printers of types
References: <20021009151317.J1703@verdot.inria.fr>
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Daniel de Rauglaudre wrote:
> 
> Hi everybody,
> 
> In Camlp4 tutorial (current version), I added a section explaining how
> to make a syntax extension which, when loaded, automatically generates
> printers of all your types:
> 
> For example, if your input file contains:
> 
>     type colour = Red | Green | Blue
> 
> this will be interpreted like this:
> 
>     type colour = Red | Green | Blue
>     let print_colour =
>       function
>         Red -> print_string "Red"
>       | Green -> print_string "Green"
>       | Blue -> print_string "Blue"


I've been working on extending this to more general types, which I
suppose would be easy for someone who's had some practice with camlp4. 
I'm running into 2 problems, and anticipating a third one.

1. Is there a clean way to handle (sum) types with constructors with
multiple module qualifications?  I hacked the example to deal with
Foo.bar, but it doesn't seem to extend automatically to Foo.Bar.baz.  As
I understand it, I'd need a new pattern for each additional uid.

2. How are tuples represented in camlp4's syntax?  This is so I can
match them when analyzing a type.

3. This is the big one.  When working on a type like:

type t = int

with the obvious extention to Daniel's code, the preprocessor produces

type t = int let rec print_t = print_int

Which the compiler rejects with "This kind of expression is not allowed
as right-hand side of `let rec'"  I haven't been able to figure out a
way to sneak it past, either.  What's going on here?  Why can't I rename
print_int?

Thanks

 - ken
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